Lubricated metallic container stocks and method of preparing the same and applying an organic coating thereto

ABSTRACT

METALLC CONTAINER STOCKS ARE LUBRICATED WITH CITRIC ACID ESTERS. THE IMPROVED LUBRICATED CONTAINER STOCKS OF THE INVENTION ARE CHARACTERIZED BY EXCELLENT WETTABILITY AND ADHESION OF ORGANIC COATINGS IN GENERAL AND ESPECIALLY EPOXY RESIN COATING COMPOSITIONS. THE CITRIC ACID ESTER LUBRICANTS ARE PHAMACOLOGICALLY SAFE AND ARE EASILY APPLIED AT LOW COST BY ELEECTROSTATIC DEOSITION AND OTHER METHODS PRESENTLY USED FOR APPLYING PRIOR ART LUBRICATING AGENTS. THE METHOD OF THE INVENTION IS ESPECIALLY USEUL IN LUBRICATING TINPLATE STRIP, BLACKPLATE STRIP, BLACKPLATE STRIP HAVING A CHROMIUM-CONTAINING COATING THEREEON, AND ALUMINUM STRIP OF CONTAINER STOCK GAUGE WITH CCITRIC ACD ESTER LUBRICANTS HAVING THE FOLLOWING STRUCTURAL FORMULA:   R1-O-CO-CH2-C(-OR4)(-CO-OR2)-CH2-CO-OR3   WHEREIN R1, R2 AND R3 ARE INDIVIDUALLY SELECTED FROM THE GROUP CONSISTING OF HYDROGEN AND ALCOHOLIC RESIDUAL CONTAINING 1-18 CARBON ATOMS, R4 IS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN AND CARBOXYLIC CID RADICALS CONTAINING 1-18 CARBON AOMS, AND AT LEAST ONE OF R1, R2 AND R3 IS AN ALCOHOLIC RESIDUE. THE INVENTION FURTHER PROVIDES A NOVEL METHOD OF APPLYING AN ORGANIC COATING ON LUBRICATED METALLIC CONTAINER STOCKS.

United States Patent LUBRICATED METALLllC CONTAHNER STOCKS AND METHOD OFPREPARING THE SAME AND APPLYlNG AN ORGANIC COATlNG THERETO John R.dmith, Richmond, and James A. Bray, Salineville, Ohio, assignors toNational Steel orporation No Drawing. Filed Mar. 10, 1972, Ser. No.233,748

lint. Cl. 844d 1/16 US. Cl. lll7--75 40 Claims ABSTRACT OF THEDISCLOSURE Metallic container stocks are lubricated with citric acidesters. The improved lubricated container stocks of the invention arecharacterized by excellent wettability and ad hesion of organic coatingsin general and especially epoxy resin coating compositions. The citricacid ester lubricants are phatmacologically safe and are easily appliedat low cost by electrostatic deposition and other methods presently usedfor applying prior art lubricating agents. The method of the inventionis especially useful in lubricating tinplate strip, blackplate strip,blackplate strip having a chromium containing coating thereon, andaluminum strip of container stock gauge with citric acid esterlubricants having the following structural formula:

wherein R R and R are individually selected from the group consisting ofhydrogen and alcoholic residual containing 1-l8 carbon atoms, R, isselected from the group consisting of hydrogen and caboxylic acidradicals containing 1-18 carbon atoms, and at least one of R R and R isan alcoholic residue. The invention further provides a novel method ofapplying an organic coating on lubricated metallic container stocks.

BACKGROUND OF THE INVENTION The present invention broadly relates toimproved lubricated metallic container stocks and to a novel method ofpreparing the same. In still another of its aspects, the inventionfurther relates to a novel method of applying an organic coating onlubricated metallic container stocks.

A thin coating of a lubricant is applied on the surfaces of mostmetallic container stocks produced in this country. The lubricant isnecessary in order to facilitate handling of sheets of the product andto protect the surfaces against abrasion, scratches, and to some extentcorrosion. If the lubricant is not applied, the individual sheets tendto stick together and do not handle well in subsequent fabricating stepsutilizing automatic machines for applying organic coatings,lithographing and manufacturing containers.

The amount of lubricant that is applied is quite small and must bemaintained within a relatively narrow critical range. If too littlelubricant is applied, then the disadvantages enumerated above when nolubricant is applied are present to some extent. If too much lubricantis applied, there is excessive slippage and it is difficult to stack andhandle the individual sheets. Excess oil may also adversely affect theapplication of organic coatings, lithographing, labeling and othersubsequent steps. The lubricant usually should be applied in an amountof about 0.05-l.0 gram per base box. The term base box is used in thisart to refer to a quantity of metallic container ice stock having atotal surface area, i.e., the surface area 0f both sides, of 62,720square inches. The term base box is used hereinafter for convenience indisclosing and claiming the invention and refers to a total surface areaof 6 2,720 square inches on which the lubricant is applied.

Lubricants may be applied to metallic container stock by a number ofmethods such as branning, dipping in a solvent solution of the lubricantfollowed by evaporating the solvent, and electrostatic deposition.Electrostatic deposition is a method that is suitable for theapplication of the small quantities of lubricant set out above in theform of a thin uniform film at high line speeds. The line speedsemployed in the manufacture of metallic container stocks sometimes varyfrom 250 feet per minute to as high as 2,000 feet per minute and amethod capable of control of the rate of lubricant application for theseline speed variations is required. As a result, the lubricant that isselected for commercial use should be capable of being applied byelectrostatic deposition.

A lubricant for lubricating metallic container stocks should possess aunique combination of properties. If any one of this combination ofproperties is missing, then the lubricant is not entirely satisfactory.As a result, only a very small percentage of the numerous potentiallubricants are satisfactory. The problem of selecting a suitablelubricant is complicated by the fact that it is often impossible topredict whether or not a specific substance will be suitable bylaboratory scale lubricating experiments and the potential lubricantmust be applied in a production run.

Some of the more important characteristics of an entirely satisfactorylubricant for metallic container stocks are as follows:

(1) In the case of electrostatic deposition, the lubricant should beeasily atomized to form a finely divided dispersion thereof in a gaseousmedium such as air. A carefully controlled quantity of the suspendedparticles of lubricant in the resultant gaseous dispersion should becapable of being electrostatically precipitated in the form of a thinuniform film upon metallic container stock moving at high line speeds.

(2) The lubricant should be retained on the container stock for areasonable period of time in an amount effective to lubricate thesurface.

(3) The lubricant should be compatible with protective and/ ordecorative organic coatings which are subsequently applied to thelubricated container stock. The lubricant also should have no effect ora beneficial effect on the wetting of the surface area to be coated andthe adhesion thereto of the protective and/or decorative organiccoatings.

(4) The lubricant should not be discolored upon heating or baking thelubricated container stock at a temperature sufficiently high to hardenor cure the organic coatings.

(5) The film of lubricant should be resistant to oxidation and notharden or lose its desirable lubricant properties over a reasonableperiod of time.

(6) The lubricant should be free of objectionable tastes and odors inthe quantities applied and under the conditions of use.

(7) The lubricant must be pharmacologically safe and nontoxic in theamounts applied as the lubricated container stocks are often used tomanufacture containers for preserving and storing foodstuffs.

A number of naturally occurring vegetable oils and synthetic esters ofcarboxylic acids have been proposed heretofore for use in lubricatingmetallic container stocks. Vegetable oils such as cotton seed oil, palmoil and the like have a tendency to oxidize to a solid film which is nolonger a good lubricant after a relatively short period of storage. Anumber of the synthetic ester lubricants have this deficiency, and as aresult of this and other advantages, several of the esters of sebacicacid have been used heretofore as lubricants. Synthetic esters ofsebacic acid prepared from alcohols containing eight or more carbonatoms, such as dioctyl sebacate, are widely used as lubricants at thepresent time. While dioctyl sebacate is one of the best synthetic esterlubricants available heretofore, it does have some deficiencies in viewof recent developments in the art. For example, a substantial percentageof the metallic container stock produced in this country is given acathodic dichromate treatment such as disclosed in US. Pats. No.3,278,401 and 3,296,106. The cathodic dichromate treatment increasescorrosion resistance and is desirable for this purpose. When thecathodic dichromate treated container stock is lubricated with dioctylsebacate or other prior art lubricants, wetting or eyeholing problemsoften occur. This tendency is especially pronounced when epoxy typelacquers and certain other advanced organic coatings are used. As aresult of this deficiency, the art has long sought a suitable lubricantwhich meets all of the requirements set out above, regardless of thetype of organic coating and Whether or not the container stock hasreceived a cathodic dichromate treatment. However, an entirelysatisfactory lubricant was not available prior to the present invention.

It is an object of the present invention to provide an improvedlubricated metallic container stock which is readily wetted by initiallyfluid organic coating materials which often present wetting problemssuch as epoxy lacquers.

It is a further object to provide a novel method of lubricating metalliccontainer stocks wherein the lubricant is an ester of citric acid.

It is still a. further object to provide a novel method of applying anorganic coating on lubricated container stocks wherein the lubricatedsurface area to be coated is easily wetted by initially fluid organiccoating materials and whereby eyeholing and other imperfections in thefinal hardened organic coating may be minimized.

Still other objects and advantages of the present invention will beapparent to those skilled in the art upon reference to the followingdetailed description.

DETAILED DESCRIPTION OF THE INVENTION IN- CLUDING PREFERRED EMBODIMENTSAND VARIANTS THEREOF The present invention provides improved metalliccontainer stock having a thin substantially uniform film of a citricacid ester lubricant on at least one surface area thereof. The citricacid ester lubricant is present in an amount to lubricate the surfacearea and preferably is present in an amount of about 0.05-1.0 gram perbase box, i.e., about 0.05-1.0 gram for each 62,720 square inches oflubricated surface area. In instances where the lubricated containerstock is to receive an organic coating in a subsequent processing step,then usually better results are obtained when citric acid esterlubricant is present in an amount of about 0.15-0.40 gram per base box.

Citric acid ester lubricants for use in practicing the invention mayhave the following structural formula:

wherein R R and R are individually selected from the group consisting ofhydrogen anl alcoholic residua containing 1-18 carbon atoms, R; isselected from the group consisting of hydrogen and carboxylic acidradicals containing 1-18 carbon atoms, and at least one of R R and R isan alcoholic residue. In some instances, it is prefered that R R and/orR, be alcoholic residua containing 1-10 and often for better results 1-4carbon atoms, and/ or that R, be selected from the group consisting ofhydrogen and carboxylic acid radicals containing 1-10 and often forbetter results 1-4 carbon atoms. In other instances, it is preferredthat each of R R and R be alcoholic residua containing 1-10 andpreferably 1-4 carbon atoms, and/or that R; be either hydrogen or acarboxylic acid radical containing 1-10 and preferably 1-4 carbon atoms.

Specific examples of presently preferred citric acid ester lubricantsinclude triethyl citrate, acetyl triethyl citrate, tributyl citrate,acetyl tributyl citrate, acetyl tri-Z-ethylhexyl citrate, and admixturesof one or more thereof. Acetyl tributyl citrate often gives the bestresults.

Any suitable prior art metallic container stock may be lubricated withthe citric acid ester lubricants of the invention. Usually tinplate,blackplate, blackplate having a chromium-containing coating thereon andmetallic aluminum of container stock gauge are the preferred containerstocks. Metallic container stocks are usually in the form of sheet orcontinuous strip, but may be in other shapes convenient for use in themanufacture of containers. Container stocks suitable for use inpracticing the invention are disclosed in numerous texts and US.patents. For example, blackplate and tinplate are disclosed in TheMaking, Shaping and Treating of Steel, 7th edition, published by theUnited States Steel Corporation and aluminum container stocks aredisclosed in the text Aluminum, published by the American Society forMetals, of which chaper 23 in volume 3, is the most pertinent.Blackplate having a chromium-containing coating thereon is disclosed inPats. No. 3,316,160, 3,526,- 486, 3,567,599, and 3,475,295. Pat. No.3,526,486 discloses blackplate having a metallic chromium-containingcoating thereon contiguous with the ferrous metal surface and anonmetallic chromium-containing film thereover which is cathodicallydeposited from an aqueous hexavalent chromium electrolyte. Thedisclosures in the above texts and patents are incorporated herein byreference.

The metallic container stocks to be lubricated may be given anelectrochemical treatment in an aqueous electrolyte containing a watersoluble chromium compound to deposit a chromium-containing film thereonwhich increases corrosion resistance. US. Pat. No. 3,278,- 401 disclosesa method of electrochemically depositing a chromium-containing film ontinplate, which preferably but not necessarily is flow brightenedelectrolytic tinplate. The chromium-containing film is cathodicallydeposited on the tinplate from an aqueous hexavalent chromiumelectrolyte. Cathodic dichromate treatment is usually preferred. Pat.No. 3,296,106 discloses the treatment of various metallic substrates toelectrochemically deposit thereon a chromium-containing film whichincreases corrosion resistance. The metallic substrates are cathodicallytreated in an aqueous hexavalent chromium electrolyte and the treatmentis effective for blackplate, iron tin alloy coated ferrous metal,tinplate and other metallic container stocks. The deposition of anonmetallic chromium-containing film on blackplate coated with metallicchromium is disclosed in Pat. No. 3,526,486. The teachings of the abovepatents are likewise incorporated herein by reference. It is understoodthat the metallic container stocks may be given an electrochemicaltreatment such as described therein, or other prior art treatments, forthe purpose of increasing corrosion resistance or for imparting otherdesirable properties prior to applying the lubricant.

The products produced in accordince with the teachings of U5. Pats. No.3,278,401 and 3,526,486 are especially desirable metallic containerstocks and thus are often preferred. The citric acid ester lubriants areespecially effective with these substrates.

Any suitable prior art method for lubricating metallic container stockmay be used for applying the citric acid ester lubricant in the form ofa thin substantially uniform film. Examples of prior art methods includeelectrostatic deposition, branning, applying a solution of the lubricantin a volatile solvent followed by evaporating the solvent, applying anaqueous emulsion of the lubricant followed by evaporating the water, andapplying the lubricant per se directly to the container stock by meansof metering rolls, spraying or the like when it is sufficiently fluid.Electrostatic deposition is usually the preferred method of applicationin the commercial production of metallic container stocks. The citricacid esters described herein are easily applied by electrostaticdeposition and have the desirable characteristics enumeratedhereinbefore. Additionally, the synthetic citric acid esters enhancewettability of the lubricated surface by the initially fluid organiccoating and reduce surface imperfections such as eyeholing. Adhesion isalso improved and the final hardened or cured organic coatings producedin accordance with the coating method of the invention exhibit excellentadherence. These beneficial effects extend to container stocks whichhave received an electrochemical treatment prior to applying thelubricant. Cathodic dichromate treatment of tinplate and other metallicsubstrates often tends to introduce wetting problems. This problem maybe eliminated by' using the citric acid ester lubricants.

In practicing the organic coating method of the present invention, anysuitable prior art fluid organic coating material may be used such asvarnishes, lacquers and enamels for metallic container stocks. Specificexamples of organic coating materials include epoxy, modified epoxy,phenolic, modified phenolic, acrylic, modified acrylic, vinyl, modifiedvinyl, alkyd and polyurethane varnishes, lacquers and/0r enamels. Priorart lithographing or printing inks which are suitable for use onmetallic container stocks for labeling and decorative purposes areconsidered to be organic coatings for the purpose of the presentinvention. The organic coating materials should be fluid initially,i.e., sufiiciently fluid to be applied by metering rolls, spraying,brushing, and direct or indirect printing or lithographing; and may varyfrom soft pastes to fluid liquids depending upon the selected method ofapplication. The initially fluid organic coating material is hardened orcured following application by, for example, evaporating solvent orbaking to produce the final organic coating. The method of applying theinitially fluid organic coating material and then hardening the same toproduce the final organic coating may be in accordance with prior arepractice. However, the metallic container stock to be coated must belubricated with a citric acid ester of the present invention. The citricacid ester lubricant assures substantially instantaneous wetting of thesurface by the initially fluid organic coating material and allows highspeed coating lines to be employed with all organic coating materialsincluding those which tend toward poor wetting properties. Additionally,the hardened or cured organic coating tends to adhere more tightly tothe citric acid ester lubricated surface and any tendency toward pooradherence is overcome and eyeholiug or other imperfections are not aproblem. Thus, the present invention overcomes the problems of the priorart when operating high speed coating lines and especially when usingorganic coating compositions which normally present wetting problems.

The foregoing detailed description of the invention and the followingspecific examples are for purposes of illustration only and are notintended as being limiting to the spirit or scope of the appendedclaims.

EXAMPLE I Tinplated strip delivered from a prior art electrolytictinplating line at a strip speed above 1,000 feet per minute is passedcontinuously through a flow brightening zone where it is flowbrightened, followed by quenching with water and a cathodic dichromatetreatment in accordance with US. Pat. No. 3,278,401. The resultingcathodic dichromate treated flow brightened tinplate is rinsed, driedand passed through an electrostatic lubricating zone at a speedcorresponding to the speed of the tinplating line. Acetyl tributylcitrate was atomized to form a finely divided gaseous suspension, andthe gaseous suspension was passed through an ionizing zone where thesuspended particles of acetyl tributyl citrate lubricant were given anelectrical charge. A stream of the gaseous suspension of ionizedlubricant particles was directed toward and electrostaticallyprecipitated on the electrically grounded moving strip in the form of athin uniform film. The lubricated tinplate withdrawn from theelectrostatic lubricating zone had 0.26 gram per base box of acetyltributyl citrate on the surface.

The lubricated flow brightened tinplated strip was sheared into sheets.The lubricated tinplate sheets handled well in automatic equipmentwithout undue abrasion or scratching and the product was used in theExamples appearing hereinafter.

EXAMPLE II A second run was made in accordance with Example I with theexception of substituting dioctyl sebacate as the lubricant for theacetyl tributyl citrate. The resulting prodnot had 0.27 gram per basebox of dioctyl sebacate lubricant on the sheet surfaces.

EXAMPLE IllI Samples of lubricated tinplate from Example I and ExampleII were stored for four months under identical conditions to determinethe amount of lubricant lost during the period of storage.

The product of Example I initially had 0.26 gram per base box of acetyltributyl citrate on its surface, and after four months of storage 0.20gram per base box. The product of Example II initially had 0.27 gram perbase box of dioctyl sebacate on its surface, and only 0.17 gram per basebox after four months of storage. It is therefore apparent that the rateof loss of acetyl tributyl citrate during storage is substantially lessthan that of dioctyl sebacate. This is an unexpectedly low rate of lossof acetyl tributyl citrate since dioctyl sebacate is considered to bevery outstanding in this respect.

EXAMPLE IV Samples of lubricated tinplate from Example I and fromExample II were tested under identical conditions with diluted lacquersto determine the effect of the two lubricants on wetting. One part ofthe lacquer was mixed with six parts of solvent and one drop of theresulting mixture was applied to the surface of a tinplate sample fromeach of Examples I and II laid horizontally on a fiat level surface. Thedrops of diluted lacquer were allowed to dry in air, and then baked fora permanent record. The area of flow of each system was measured insquare inches and the results recorded.

In one run, one part by volume of epoxy lacquer was diluted with sixvolumes of isophorone and the mixture was tested as set out above. Thismixture gave an area of flow of 0.24 square inch for the dioctylsebacate oiled tinplate, and 2.4 square inches for the acetyl tributylcitrate oiled tinplate.

In another run, one part of epoxy lacquer was diluted with six parts ofdiacetone alcohol and the mixture was tested as set out above. Thedioctyl sebacate oiled tinplate had an area of flow of 0.17 square inchand the acetyl tributyl citrate oiled tinplate had an area of flow of0.95 square inch.

In a further run, one part of epoxy lacquer was diluted with six volumesof ethylene glycol monoethyl ether acetate and the mixture was tested asset out above. The dioctyl sebacate oiled tinplate had an area of flowof 0.62 square inch, and the acetyl tributyl citrate oiled tinplate hadan area of flow of 2.1 square inches.

In a further run, one part of epoxy lacquer was diluted with six partsof ethylene glycol monoethyl ether and the mixture was tested as set outabove. The dioctyl sebacate oiled tinplate had an area of flow of 0.6square inch, and the acetyl tributyl citrate oiled tinplate had an areaof flow of 1.9 square inches.

It is clear from the above data that the acetyl tributyl citrate oiledtinplate was much more easily wetted by the various diluted epoxylacquers than the dioctyl sebacate oiled tinplate.

EXAMPLE V Individual runs were made using the lubricated product fromExample I and the lubricated product from Example II in a high speedline for lacquering and lithographing the sheets. The organic coating,which was used in both runs, was an epoxy lacquer which exhibited atendency toward eyeholding and poor wetting.

No problems were experienced with respect to eyeholing and wetting whenthe lubricated product of Example I, i.e., the acetyl tributyl citratelubricated tinplate was being run. However, the lubricated product ofExample II, i.e., the dioctyl sebacate lubricated tinplate exhibitedeyeholding and wetting problems and was not satisfactory in theserespects. The hardened film of epoxy lacquer on the product of Example Iwas also more adherent than on the product of Example II.

Upon making further runs identical with those of Examples I through Vabove with respect to the oiling step, except for substitutingblackplate, blackplate having a chromium-containing coating and aluminumsheet for the tinplate of Examples I through V in the oiling step,comparable results are obtained. In each instance, the acetyl tributylcitrate lubricated container stock exhibits better wetting propertiesand the hardened organic coating films applied thereto are more adherentthan when dioctyl sebacate is the lubricant.

We claim:

1. A metalic container stock having a thin substantially uniform film ofa citric acid ester lubricant on at least one surface area thereof, thesaid citric acid ester lubricant consisting essentially of at least onecitric acid ester of an alcohol containing 1-10 carbon atoms and beingpresent in an amount of about 0.051.0 gram for each 62,720 square inchesof lubricated surface area.

2. The lubricated container stock of claim 1 wherein the citric acidester lubricant is present in an amount of about 0.15-0.40 gram for each62,720 square inches of lubricated surface area.

3. The lubricated container stock of claim 1 wherein the container stockis selected from the group consisting tinplate, blackplate, blackplatehaving a chromiumcontaining coating thereon, and metallic aluminum ofcontainer stock gauge.

4. The lubricated container stock of claim 3 wherein the container stockis blackplate.

5. The lubricated container stock of claim 3 wherein the container stockis blackplate having a chromiumcontaining coating thereon.

6. The lubricated container stock of claim 3 wherein the container stockis metallic aluminum of container stock gauge.

7. The lubricated container stock of claim 3 wherein the container stockis tinplate.

8. The lubricated container stock of claim 1 wherein the said filmconsists essentially of at least one citric acid ester lubricant havingthe structural formula:

wherein R R and R are individually selected from the group consisting ofhydrogen and alcoholic residua containing 1-10 carbon atoms, R isselected from the group consisting of hydrogen and carboxylic acidradicals containing 110 carbon atoms, and at least one of R R and R isan alcoholic residue.

9. The lubricated container stock of claim 8 wherein R R and R arealcoholic residua containing 14 carbon atoms.

10. The lubricated container stock of claim 8 wherein R R and R arealcoholic residua containing 1-4 carbon atoms, and R is selected fromthe group consisting of hydrogen and carboxylic acid radicals containing1-4 carbon atoms.

11. The lubricated container stock of claim 8 wherein the citric acidester lubricant consists essentially of at least one substance selectedfrom the group consisting of triethyl citrate, acetyl triethyl citrate,tributyl citrate, acetyl tributyl citrate, acetyl tri-Z-ethylhexylcitrate, and admixtures thereof.

12. The lubricated container stack of claim 8 wherein the citric acidester lubricant consists essentially of acetyl tributyl citrate.

13. The lubricated container stack of claim .8 wherein the citric acidester consists essentially of acetyl tributyl citrate and is applied inan amount of about 0.15-0.40 gram for each 62,720 square inches oflubricated surface area.

14. The lubricated container stock of claim 3 wherein the containerstock is tinplate and the said film comprises at least one citric acidester lubricant having the structural formula:

CHz( 3OR3 wherein R R and R are individually selected from the groupconsisting of hydrogen and alcoholic residua containing 1-10 carbonatoms, R is selected from the group consisting of hydrogen andcarboxylic acid radicals containing l-10 carbon atoms, and at least oneof R R and R is an alcoholic residue.

15. The lubricated container stock of claim 14 wherein the citric acidester lubricant is present in an amount of about 0.150.40 gram for each62,720 square inches of lubricated surface area.

16. The lubricated container stock of claim 14 wherein R R and R arealcoholic residua containing 1-4 carbon atoms.

17. The lubricated container stock of claim 14 wherein R R and 'R arealcoholic residua containing 1-4 carbon atoms, and R is selected fromthe group consisting of hydrogen and carboxylic acid radicals containing1-4 carbon atoms.

18. The lubricated container stock of claim 14 wherein the citric acidester lubricant comprises at least one substance selected from the groupconsisting of triethyl citrate, acetyl triethyl citrate, tributylcitrate, acetyl tributyl citrate, acetyl tri-2-ethylhexyl citrate andadmixtures thereof.

19. The lubricated container stock of claim 14 wherein the citric acidester lubricant comprises acetyl tributyl citrate.

20. The lubricated container stock of claim 19 wherein the citric acidester lubricant is present in an amount of about 0.15-0.40 gram for each62,720 square inches of lubricated surface area.

21. In a method of applying an organic coating to metallic containerstock wherein a layer of an initially fluid organic varnish, lacquer orenamel for the container stock is applied to at least a portion of thesurface area of the container stock and thereafter the layer of theinitially fluid organic varnish, lacquer or enamel is hardened to formthe said organic coating, the improvement which comprises improving thewettability of the said surface area of the container stock by theinitially fluid organic varnish, lacquer or enamel by employing thereonas the said lubricant a substantially uniform film consistingessentially of a citric acid ester of an alcohol containing 1-10 carbonatoms, the citric acid ester being present in an amount of about 0.051.0gram for each 62,720 square inches of lubricated surface area of thecontainer stock.

22. The method of claim 21 wherein the citric acid ester lubricant ispresent in an amount of about 0.15- 0.40 gram for each 62,720 squareinches of lubricated surface area.

23. The method of claim 21 wherein the metallic container stock isselected from the group consisting of tinplate, blackplate, blackplatehaving a chromium-containing coating thereon, and metallic aluminum ofcontainer stock gauge.

24. The method of claim 23 wherein the container stock is blackplate.

25. The method of claim 23 wherein the container stock is blackplatehaving a chromium-containing coating thereon.

26. The method of claim 23 wherein the container stock is metallicaluminum of container stock gauge.

27. The method of claim 23 wherein the container stock is tinplate.

28. The method of claim 21 wherein the citric acid ester lubricant hasthe structural formula:

wherein R R and R are individually selected from the group consisting ofhydrogen and alcoholic residua containing 1-10 carbon atoms, R, isselected from the group consisting of hydroben and carboxylic acidradicals containing 1-10 carbon atoms, and at least one of R R and R isan alcoholic residue.

29. The method of claim 28 wherein R R and R are alcoholic residuacontaining 1-4 carbon atoms.

30. The coated metallic container stock prepared by the method of claim21.

31. The method of claim 21 wherein the citric acid ester lubricantcomprises at least one substance selected from the group consisting oftriethyl citrate, acetyl triethyl citrate, tributyl citrate, acetyltributyl citrate, acetyl tri-Z-ethylhexyl citrate, and admixturesthereof.

32. The method of claim 21 wherein the citric acid ester lubricantcomprises acetyl tributyl citrate.

33. The method of claim 21 wherein the citric acid ester comprisesacetyl tributyl citrate and is applied in an amount of about 0.15-0.40gram for each 62,720 square inches of lubricated surface area.

34. The method of claim 21 wherein the citric acid ester is of analcohol containing 1-4 carbon atoms.

35. The method of claim 23 wherein the container stock is tinplate andthe citric acid ester lubricant has the structural formula:

wherein R R and R are individually selected from the group consisting ofhydrogen and alcoholic residua containing 1-10 carbon atoms, R isselected from the group consisting of hydrogen and carboxylic acidradicals containing 110 carbon atoms, and at least one of R R and R isan alcoholic residue.

36. The method of claim 35 wherein the citric acid ester lubricant ispresent in an amount of about 0.15- 0.40 gram for each 6 2,720 squareinches of lubricated surface area.

37. The method of claim 35 wherein R R and R are alcoholic residuacontaining 14 carbon atoms.

38. The method of claim 35 wherein R R and R are alcoholic residuacontaining 1.4 carbon atoms, and R is selected from the group consistingof hydrogen and carboxylic acid radicals containing; 1-4 carbon atoms.

39. The method of claim 35 wherein the citric acid ester lubricantcomprises at least one substance selected from the group consisting oftriethyl citrate, acetyl triethyl citrate, tributyl citrate, acetyltributyl citrate, acetyl tri-2-ethylhexyl citrate, and admixturesthereof.

40. The method of claim 35 wherein the citric acid ester lubricantcomprises acetyl tributyl citrate.

References Cited UNITED STATES PATENTS 2,884,338 4/1959 Jenison 117-682,370,300 2/ 1945 Farrington 252-56 R 2,146,885 2/1939 Dempsey 205-212,503,217 4/1950 Prust 204-37 2,573,882 11/1951 Waters 117-68 2,573,88311/1951 Waters 117-68 2,666,716 1/1954 Kadell 117-68 2,918,390 12/1956Brown 117-71 1,993,737 3/1935 De Witt et al. 252-56 S 1,993,738 3/1935De Witt et al. 252-56 S 3,057,892 10/1962 De Groote 252-56 S 3,058,91310/1962 Koch et al 252-56 S WILLIAM D. MARTIN, Primary Examiner W. R.TRENOR, Assistant Examiner US. Cl. X.R.

29-195; 117-68, 93.4 R, 127, 134, 16 7; 148-6, 6.3; 204-37; 252-56 R,56' S UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OFCORRECTION PATENT NO. 3', 826,675

DATED July 30, 1974 INVENT0R(5) 1 John R. Smith and James A. vBray It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as'shown below:

Column 8, line 30,; change "the said" to --a--. Column 8, line 30,change "comprises" 120 -comprising--.

Signzd and Scalcdfhis I A rtesr:

GERALD J. MOSSINGHOFF Arresting Officer Commissioner of Patents andTrademarks

